The present invention relates to a method of removing sulfur and arsenic from cobaltiferous ores, and more particularly, to a method which results in the formation of a negligible amount of undesirable arsenic sulfide and/or arsine.
Cobalt occurs naturally combined with a large number of different elements. The present invention relates to a method for treating ores which not only contain cobalt, but also significant amounts of arsenic and sulfur. Two major complex arsenic sulfide ores are arsenopyrite [(Fe,Co)AsS] and cobaltite [(Co,Fe)AsS]. A number of methods have been suggested in the prior art for removing the arsenic and sulfur from such ores. One of the older techniques for removing arsenic is to subject the ore to roasting conditions whereby the arsenic is evolved as arsenious acid, after which the ore, in one way or another, is treated further, generally by smelting. The formation of the arsenious acid is a distinct disadvantage of this method since it is extremely poisonous and is difficult to sell as a product.
Processes for vaporizing the arsenic from the ore with chlorine have been suggested and operated commercially, but these are expensive also. It is well-known that arsenic can be easily eliminated when the arsenide is smelted along with a large amount of a sulfide ore, but this results in a dilution of the cobalt with a large amount of iron and/or copper. Therefore, this technique is not very economical unless the iron and/or copper subsequently can be separated from the cobalt.
Procedures also have been described for removing arsenic and sulfur by heating the ore under reducing conditions. In this technique, however, the formation of As.sub.2 S.sub.3, As.sub.2 S.sub.2 and AsH.sub.3 is unavoidable. The first two compounds lead to operational difficulties due to stickiness, and the third compound, arsine, is an undesirable gaseous poison that should be avoided as much as possible.